Just started having this issue with my macbook. I tried to install Adobe Photoshop cs6 and it froze near the start of the installation and then the mac turned off. Now I cant get onto the desktop to try and change any of the settings or to reinstall the OS. Things I am thinking it could be are... - Overheating as the mac hasnt been cleaned in 4 years and I live with quite a few cats - Crack in the solder between the processor and the motherboard due to constant heating and cooling - Possibly a virus of some kind from the software? Things I'd like to try are booting into the BIOS (or whatever its called on a mac) to alter the fan speeds to see if the problem alleviates, then I know all I have to do is give it a clean or, failing that, reinstall the OS to clarify it isnt a software issue. Can anyone help me with those ideas? Or does someone have any other better suggestions? Anything would be most appreciated at the moment!